The hint with the bridge discussion was the key. After that i a found a github discussion about network:
https://github.com/systemd/systemd/issues/969
After this i checked all networkd options and found:
https://www.freedesktop.org/software/sy ... twork.html
If i set
in the network part of the config file the vlan device will not get an IPv6 address ... problem solved.LinkLocalAddressing=no
So again, thanks for your help
Silvio